1. Field of the Invention
The invention relates to catheters used in the medical field and particularly endotracheal tubes.
2. Description of the Prior Art
Medico-surgical tubes may assume a variety of sizes, shapes and be provided with a variety of fluid openings, balloons or cuffs, couplings, or the like. Terminology applied to such devices by users, e.g. physicians, surgeons, hospitals, etc. frequently refer to them as catheters, e.g., rectal catheters, urethral catheters, hemostatic catheters and the like but in other cases they are referred to as tubes, e.g. endotracheal tubes, feeding tubes, suction tubes, drain tubes, and the like. For the sake of brevity in describing the improved devices of the invention and their method of production, the term "catheter" is employed throughout the specification and accompanying claims to encompass pertinent medico-surgical devices whether they be popularly referred to by the medical profession and other users as "catheters" or "tubes".
The modern trend in medical and surgical practices is toward the use of disposable catheters, i.e., those which may be used a single time on one patient and then discarded. Catheters of this type normally involve a plurality of lumens, one being the major lumen which serves to convey urine, blood serum, gases or any other fluid which may be introduced into or removed from the body of the patient and frequently a secondary lumen which is used as a conduit for air or liquid employed in inflating a balloon which forms a portion of the distal end of the catheter. Such a secondary lumen is attached to an inflation tube through which the air or liquid used to inflate the catheter balloon is introduced. These catheters, although providing a number of improvements over catheters which have existed before, suffer from some inadequacies particularly with the number or variety of functions that can be performed with a specific catheter.
Particularly when one is concerned with high frequency ventilation there is required the ability to provide oxygen or other gases at high rates and smaller tidal volumes, and it is often desirable to measure the pressure of the oxygen or other gas being emitted at the catheter distal end and to irrigate the vicinity for removal of fluids and other debris in the trachea. High frequency ventilation is a new technique in respiratory care which involves the ventilation of patients at higher rates and with smaller tidal volumes. This reduces peak and mean airway pressures encountered during mechanical ventilation and may facilitate the diffusion of gases across the alveolar capillary membrane. This technique has been called high frequency positive pressure ventilation (HFPPV), high frequency jet ventilation (HFJV) or high frequency oscillation (HFO) depending on the ventilatory rate employed and all of these techniques are generally known as high frequency ventilation (HFV).
With high frequency ventilation, particulary HFPPV and HFJV, as well as jet ventilation at conventional rates, the gases have been traditionally delivered through a transtracheal catheter inserted percutaneously or through a relatively small bore 10-14 (FR) insufflation catheter inserted orally or nasally until the distal tip is below the cords. In either case expired gases are allowed to passively escape past the indwelling cuffless catheter. Some studies have suggested that during high frequency ventilation the fresh gases should be introduced as close as possible to the carina for optimal gas exchange. This would indicate that the opening for any insufflation passage delivering these gases should be at the distal tip of the tube. However, there are disadvantages associated with this configuration. These include the alignment and direction problem associated with the location contiguous with the carina. For example, slight rotation of the tube can result in uneven ventilation of both lungs. Also, the exit of gases from the insufflation passage at high velocity may cause damage to the trachea mucosa. During the injection of gases entrainment can result in the generation of negative airway pressures in the region of the tube proximal to and immediately surrounding the insufflation lumen opening. Consequently, if there is a provision with the catheter to monitor airway pressure it should be measured sufficiently downstream or distal to the insufflation opening to minimize or eliminate the effect of entrainment and enhance the monitoring and irrigation function.
In the catheter described herein many of the problems discussed above have been eliminated or at least minimized by providing a multi-purpose device. The catheter is like a conventional tracheal tube except that it incorporates an insufflation passage or lumen within its wall. An additional lumen may be provided for irrigation or for monitoring airway pressure. In cuffed tubes the insufflation and irrigation/monitoring lumens are in addition to and generally larger than the secondary lumen provided for cuff inflation. The tube is configured such that the distal opening for the insufflation passage is displaced somewhat from the tip of the tube to avoid the distribution problem discussed above and to protect the patient from potential damage or trauma of high velocity gases. When the irrigation/monitoring lumen is included, its opening is located distal to the opening of the insufflation lumen and significantly spaced therefrom. If the pressure monitoring passage opening were located substantially closer to the opening for the insufflation lumen the pressure readout would be unusually low as a measure of entrainment present during the high velocity flow of the gas exiting from the insufflation lumen.
Another advantage of the multi-purpose catheter of the invention with the pathways for insufflation gases and for monitoring and irrigation is that there is always guaranteed a pathway for expired gases through the primary passage. Also, solutions delivered through the irrigation/monitoring passage or lumen can be effectively nebulized by the high velocity gas flow delivered through the insufflation passage or lumen. This configuration with the primary lumen also provides for scavenging of anesthestic gases, and positive end expiratory pressure (PEEP) can be maintained at any set level. This system also provides for additional aspiration protection through the use of a tracheal cuffed tube although for pediatric or neonatal applications the cuff is not necessary. By providing the additional lumen or lumens within the tube described above, it is a relatively simple matter to change to conventional therapy should that become necessary for whatever reason.
By having the passages or lumens extruded into the tube and otherwise configured as described above, a number of disadvantages are overcome. Certain problems have been associated with standard tracheal tubes where two cannulas have been passed through an external connector and into the main lumen of the tube. This latter approach compromises the cross-sectional area of the primary lumen. It becomes cumbersome and awkward to work with the number of tubes involved. And, the exact location of the distal tip of each cannula is difficult to ascertain. The patient must be disconnected from ventilatory support during suctioning or bronchoscopies. In this regard virtually all intubated patients need to be suctioned to remove accumulated secretions. While this procedure is being performed, the patient must be disconnected from ventilatory support or cumbersome external connectors must be employed. In critically ill patients, the oxygen evacuated from the lungs during suctioning, particularly at a time when no ventilatory support is possible, can result in serious hypoxia. If irrigation of the tracheal bronchial tree to aid the removal of secretions is necessary, the ventilator can be disconnected even longer. The multipurpose tracheal tube of the invention permits the delivery of air or oxygen by constant insufflation, jet ventilation, or HFV through the insufflation lumen during suctioning, thus preventing undesirable hypoxia. The irrigation can easily be accomplished using the irrigation/monitoring lumen.